1. Field of the Invention
The present invention relates to an improved injection molding apparatus and method whereby a self aligning articulated coupling allows molten material to be transmitted between an injection unit and a hot runner system in a movable mold component, in order to accommodate the slight movements between the injection unit and the hot runner system caused by thermal elongation of the heated components as well as due to ambient molding conditions.
2. Description of Related Art
In some injection molding applications, the material being molded may lose desired properties if it is exposed to oxygen during molding processes, such as, for example, by parts disconnecting at the interface between the injection unit and the hot runner system. Consequently, in these applications there is a need for the injection unit of the molding machine, in which the material is plasticized, to be continuously sealed to the hot runner system of the mold that is distributing the material to the mold cavity or cavities. It is also desirable for the injection unit to remain directly connected and sealed to the mold or machine's movable section (containing the material infeeding port) throughout the mold's traveling portion of the molding cycle. This is especially true in some multi-material injection molding applications where one of the injection units moves with the movable portion of the mold. This movement, together with ambient molding conditions such as vibration, heat cycling, metal fatigue, etc., may cause damage at the interface between the injection unit and the hot runner system, leading to a leak of melt under high pressure.
U.S. Pat. No. 4,243,362 to Rees and U.S. Pat. No. 4,444,711 to Schad both disclose multi-material turret injection molding machines having one of their two injection units mounted on the machine's movable platen and directly connected to that portion of the mold that is mounted to the movable platen with a conventional sealing nozzle/bush interface. The nozzle remains sealed and connected to the mold infeeding port throughout the molding cycle by virtue of the injection unit being mounted on top of the moving platen and traveling therewith.
Japanese Publication 61-121912 to Shoichi discloses a multi-material injection molding machine having two injection units that connect to hot runners mounted within intermediate movable platens via nozzles. There is no disclosure that the injection units remain sealed to the hot runners throughout the molding cycle. However, it can be inferred from the figures that if the injection units do not maintain a sealed connection throughout the molding cycle they must move into and out of a sealing engagement with hot runners so that sufficient clearance can be provided to allow the movable platens to move when the molds open.
PCT publication WO 99/36244 to Rivi, discloses an injection unit mounted on a mold and maintaining a sealed connection to the mold's infeeding port throughout the molding cycle.
PCT publication WO 02/22340 to Schuett discloses an injection molding machine having a single injection unit slidably mounted alongside and parallel to the clamp mechanism that is releasably sealed to the molds' infeeding ports by a cylinder that also maintains the sealed relationship throughout the molding cycle. The cylinder disconnects the injection unit from the molds' infeeding ports and repositions the injection unit into a special location for purging. There is no disclosure of any sealing features or self aligning features of the injection unit.
U.S. Pat. No. 3,718,166 to Gordon discloses an injection molding machine with multiple nozzles that are pivotably mounted in a manifold. Each nozzle body includes a spherical mounting in the manifold to allow it to pivot with respect to its alignment with the manifold. Although springs are used to urge the nozzles toward the mold interface, there is no disclosure of springs being used to urge the mating halves of the spherical seats toward the spherical feature on the nozzle bodies. An adjusting screw is used to perform this function and thereby provides no automatic adjustability. Thus, at various operating temperatures, differing amounts of thermal expansion in the components provide the potential for material leakage or moving part seizing at the spherical interface with the melt channel.
U.S. Pat. No. 4,702,689 to Schmidt discloses a pivotable hot runner nozzle that can be rotationally oriented to align with a mold cavity surface while maintaining a sealed connection to the hot runner manifold. Once the nozzle has been manually aligned, it is clamped in position and it can no longer re-align with any subsequent movement of the components.
U.S. Pat. No. 5,540,580 to Takada discloses a hot runner connection to a machine nozzle having a rotatable connection through which the melt channel passes. There is no disclosure of the injection unit being connected by bolts or the like to the hot runner, and therefore the motion of the hot runner would not cause the injection unit to follow.
Thus, what is needed is a self-aligning injection apparatus and method that will allow an injection unit to remain reliably sealed to the hot runner system in a movable mold section throughout the mold's traveling portion of the molding cycle, and is easy to install, maintain, and service.